The present invention relates to an electrodynamic speaker, and more particularly to a miniature, thin and cost-saving electrodynamic speaker with excellent working property of fabrication and a highly efficient magnetic circuit.
FIG. 1 shows the structure of a conventional electrodynamic speaker. The speaker is fabricated in the following order in FIG. 1. A voice coil 5 is secured to a vibrating plate 1. Then a yoke 7, on which a magnet 8 and a pole piece 9 are mounted, is secured to a frame 2. The peripheral portion of the vibrating plate 1 is secured to the frame 2. A lead terminal 6 of the voice coil 5 is fixedly secured to a lead substrate 3 positioned on the lower surface of the frame 2 through a back hole 4 thereof. This structure has the following drawbacks:
(1) Since the voice coil 5 is secured on the thin and easily deformable vibrating plate 1, the voice coil cannot be positioned with accuracy.
(2) Non-uniformity of the clearance between the peripheral portion of the vibrating plate 1 and the frame 2 in the diametrical direction causes a variation in the voice coil position when the vibrating plate 1 is secured to the frame, whereby the voice coil 5 may sometimes be in contact with the pole 9 or the yoke 7.
(3) It takes time to lead the lead terminal 6 of the voice coil 5 through the back hole 4 to the lower surface of the frame 2.
(4) The fragile vibrating plate with the voice coil should be handled with great care since the lead terminal has not been attached.
As illustrated, the accurate positioning of the voice coil and the magnetic circuit is not ensured and the attachment of the voice coil terminal to the lead substrate takes time and is done during the course of securing the frame on which the magnetic circuit is mounted to the vibrating plate on which the voice coil is mounted.
The dimension of a magnetic gap and the position of the voice coil largely affect the efficiency and distortion of the electrodynamic speaker, and thus a speaker with high quality can not be realized without improving these aspects. For cost reduction, on the other hand, the fabrication process, such as securing of the voice coil, attachment of the lead terminal, and regulation of the magnetic gap by use of a jig for inserting the voice coil therein, should be improved.
To miniaturize a speaker, a vibrating member should be thinly made for reproducing a low sound in view of the reproduction frequency zone. Since miniature speakers are mostly used for portable devices, most vibrating plates are formed of a humidity-resistant polyester seat material by thermal pressure molding, as shown in FIG. 1. The accuracy of dimension of the vibrating plate is unstable as the vibrating plate is thin and subjected to the bending work, and the portion serving as a side in mounting the coil is hard to find. Further, the 8.OMEGA. resistance value, equivalent to the conventional type, cannot be obtained by the miniature speaker unless the wire for the voice coil is thinly made. Accordingly, great care should be taken in shifting the process without securing the voice coil terminal and thus it is preferable to treat the voice coil terminal in the same process as mounting the voice coil.
Generally, the effective diameter of a vibrating plate of a speaker largely affects its efficiency, and thus the efficiency of a miniature speaker necessarily deteriorates. Since a miniature portable device, however, operates on a limited power source, it is necessary to have a highly efficient speaker for use in portable devices. In view of the foregoing, the efficiency of the magnetic circuit portion, especially the dimension around the magnetic gap, is a very important point.
FIG. 2 shows another conventional embodiment. The voice coil terminal 6 is led to the peripheral portion of the vibrating plate 1 from where the voice coil is mounted, and connected to the lead substrate 3 provided on the lower surface of the frame 2 through a notched recess 10 at the side surface of the frame 2. In this structure the lead terminal should be carefully secured to the lead substrate lest an abnormal sound should be produced by contact of the lead terminal with the vibrating plate. Therefore this embodiment is not suitable for a miniature and cost-saving speaker because the fabrication or assembly order is identical to that of FIG. 1, and thus the same drawbacks will occur.